The invention described herein relates to nuclear reactors and particularly to a filter used for removing debris from the reactor and primary loops during cold hydrostatic and hot functional testing.
During manufacture and subsequent installation of components comprising a nuclear reactor coolant circulation system, diligent effort is made to help assure removal of all debris from the reactor vessel and its associated systems which circulate coolant therethrough under various operating conditions. Conventionally, the debris is removed during cold hydrostatic and hot functionl testing which is performed to verify the correct functioning and structural adequacy of the primary coolant system and reactor core support structure before loading of the actual fuel assemblies and control rods in the pressure vessel.
This debris in the form of metal chips and shavings, small solid sections of metal, and the like, comprises the residue of machining, welding and fitting operations performed during the time the reactor vessel and associated systems are being manufactured and assembled into an operable plant. Although elaborate procedures are carried out to help assure debris removal, experience shows that in spite of the safeguards used to effect such removal, some chips and metal particles still remain hidden in the systems.
Different methods are used for effecting such debris removal. In small reactors, a single assembly of screens of the proper strength and characteristics is placed over the coolant inlet to the reactor core. As coolant is circulated through the reactor vessel during testing, such foreign matter which may reside in the system are caught by the screens and then later removed when the testing phase has been completed. Although single assembly screens are effective for small reactors, they cannot be used with large reactors because constant flow forces imposed on the screens are so large that the screen elements fracture and screen particles then circulate in the system. In other methods, no screens are used since the geometry of the steam generator and bottom of the reactor pressure vessel serves as a catch basin for such particles which also are removed after functional testing. However, small particles which may remain in the system can cause malfunction of operating parts if lodged between control rods and a guide tube, for example, or in the operating components of a pump.